Method and apparatus for leveling self-frecting platform structures



June 23, 1970 3,516,513

METHOD AND APPARATUS FOR LEVELING SELF-BRECTING NVEMTORJ Dean J. lgoer'fi r Carroll Wage/Q00):

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United States Patent O US. Cl. 182-19 8 Claims ABSTRACT OF THE DISCLOSURE For use with self-erecting platforms, a method and apparatus for leveling are described in which electrical sensing probes are positioned with respect to a common horizontal plane as determined by an electrically conductive fluid so as to provide a corrective response from either make or break contact when a portion of the plat form leads in raising or lowering movement.

The present invention relates to leveling means for self-erecting platform structures, and in particular to a horizontal leveling system utilizing the surface of a liquid medium as a reference plane.

Self-erecting systems for raising and lowering relatively heavy and complex engineering equipment have been known for some time. In the Madsen Pat. No. 1,715,853 for Proportioning Apparatus, issued June 4, 1929, a self-erecting bin or receptacle is shown which is raised into position on pairs of legs so that a vehicle can be driven beneath it. The bin is divided into compartments into which different grades of gravel or other aggregate are placed and discharged into a dispensing hopper as needed. Each of the four legs which support the bin contains an individually operatable mechanical jack. The entire apparatus can be transported in the collapsed condition by truck to the site, whereupon the legs are lowered to the ground and the bin is raised into position by means of the jacks. The hopper or other weighing or dispensing device is then attached and the apparatus is ready for use.

Today, the use of mechanical hand-operated raising means is on longer acceptable. Larger and more complex installations, such as the relatively heavy dispensing and mixing equipment utilized in self-erecting equipment such as transportable asphalt mixing plants, require the use of power raising and lowering means. The total weight of such units makes impractical the use of a single common synchronized chain and sprocket, gear and pinion, cable and pulley, or other mechanical actuating means. Instead, individual power means are required for each of the supporting elements of the structure. Hydraulic power means has been found to be the most satisfactory for this application.

But when a separate hydraulic power means is used in each of the individual vertical supports, uniform movement of each power means cannot be assured because slight differences in hydraulic pressure between cylinders and frictional losses in the cylinders combine to result in different rates of raising and lowering. Also, variations in the weight carried by each of the support elements having a hydraulical actuator will result in different rates of movement with a given amount of input hydraulic pressure.

Whatever power means is used, separate control of the raising and lowering apparatus in each of the supporting elements of the structure is necessary to prevent binding, tilting, or canting of the equipment as it is raised and lowered. As in the Madsen patent mentioned previously, most self-erecting strutcures utilize a platform on i'ice which the equipment to be raised or lowered is attached, with the paltform being guided for raising and lowering movement in ways or slides on the vertical supporting elements of the structure. A small variation from proper alignment during raising and lowering is often enough to cause binding and seizing which, if not immediately corrected, can lead to damage to the equipment.

In view of the foregoing, it is a principal object of the present invention to provide a leveling system for use in self-erecting platform structures which assures a constant relative rate of movement for all parts of the structure during both raising and lowering operations. For this purpose, it is intended that the leveling system be effective to control the individual power means which effect raising and lowering of the various portions of the platform structure.

It is further intended to provide a method of operation in which any portion of a self-erecting platform structure which leads any other portion in raising or lowering is effective to cause a control signal which limits the rate of movement of its associated power raising and lowering means until the variation has been corrected and the platform returns to level movement.

A further object is to provide apparatus for use with a self-erecting platform structure which makes use of a fixed reference level as determined by an electrically conductive liquid, and in which variations from the desired reference level are detected by adjustable electrical probes which are associated with individual raising and lowering power means.

Other objects and advantages of the invention will become apparent upon reading the fo owing detailed description and upon reference to the drawings, in which:

FIG. 1 is a combined partial perspective and schematic diagram of a leveling system embodying the present invention, with a typical hydraulic raising and lowering system and associated hydraulic circuit being shown in connection with a platform guided for raising and lowering movement;

FIG. 2 is a schematic electrical circuit diagram of the control system used in connection with the apparatus of FIG. 1;

FIG. 3 is a fragmentary elevation of the platform and hydraulic structure shown in FIG. 1, with the platform being shown canted a few degrees from a desired horizontal level;

FIG. 4 is an enlarged elevation in partial section of a level sensor as shown in the preceding figures; and

FIG. 5 is a fragmentary view similar to FIG. 4 showing the probe of the sensor adjusted to an immersed position in the conductive liquid.

Although the invention will be described in connection with particular exemplary embodiments and procedures, it will be understood that it is not intended to so limit the invention, but it is instead intended to cover all alternative and equivalent constructions, methods, and procedures as may be included within the spirit and scope of the invention as defined by the appended claims.

Referring to the drawings, there is shown in FIG. 1 a hydraulic raising and lowering system in which level control is accomplished by means of the present invention. Shown in perspective is a platform structure 10 which is rigidly fabricated from steel beams, but which, because of its size or the loads which it must bear, is susceptible to canting or tilting during raising and lowering movement. The platform 10 is carried by four individual vertical supports 11 which are firmly supported on the ground by means of pads 12 (FIG. 3), or other suitable means. The vertical supports 11 may be braced in any desired way, either by cross-bracing as shown in the Madsen patent previously mentioned or by angle sup ports extending outward from the structure, but for purposes of clarity such supplementary reinforcements have been omitted from the present illustrations.

At each corner of the platform there is attached a slide or shoe 13 which is retained by and slidable within its adjacent vertical support 11. It can be seen that the supports 11 thus form a vertical track in which the slides 13 are guided for raising and lowering movement of the platform 10.

Individually controllable hydraulic cylinders 15 are carried by the supports 11 and operably attached to the individual slides 13. Each cylinder 15 is connected by a pressure line and a return line to a manual control valve 17 through an electrically controlled cut-off means consisting of a solenoid control valve 16. Operating the manual valve 17 in one direction causes raising movement of its associated hydraulic cylinder 15, while operation in the other direction releases pressure and results in lowering of that cylinder. A common hydraulic pressure pump 18 directs pressure fluid to the manual valve 17, and a common drain 20 and reservoir 21 are also provided.

As a principal feature of the invention, the platform 10 is equipped with apparatus which provides a constant reference level by means of a conduit containing an electrically conductive fluid. Electrical probes are then used to pick up variations of platform position from the desired reference level. For this purpose an individual level sensor 22 is provided adjacent each support 11 for the purpose of controlling the hydraulic cylinder 15 associated with that portion of the platform 10. Interconnecting each of the sensors 22 is a continuous length of conduit 23 containing an electrically conductive fluid, such as salt solution.

As best shown in FIG. 4, each of the sensors 22 includes a sensing chamber 25 and an electrical probe 26, with the conduit 23 being connected to the chamber 25 by means of an elbow fitting 27 so that the sensor 22 may extend in the vertical direction. The sensing chamber 25 contains a sight glass 28 through which the electrically conductive fluid is visible through side apertures 30 in the chamber. The chamber 25 is sealed at top and bottom by threaded fittings 31, 32, with the upper fitting 31 having an inserted upraised collar 33 over which a slidable hood or cap 35 is fitted. The probe 26 is secured to the slidable cap 35, and insulated therefrom by an insulating block 36. Thumb screws 37 are threaded to the cap 35 and engage the collar 33 so that the height of the probe 26 relative to the sensing chamber 25 may be easily adjusted by loosening the thumb screws 37, adjusting the cap 35 and probe 26 to the desired level, and retightening the thumb screws.

Electrical connections are made to the sensor 22 by means of a probe lead 38 attached to the upper tip of the probe 26 which protrudes through the cap 35, and by a ground lead 40 attached to the elbow fitting 27.

Pursuant to the invention, means are provided for regulating the hydraulic cylinders 15 in such a way that if one corner of the platform 10 leads the others during either raising or lowering movement, a change in electrical continuity is sensed at its associated sensor 22 which results in the momentary interruption of power to that cylinder until the platform level is corrected. This is accomplished for lowering movement of the platform 10 by visually adjusting the position of each probe 26 with respect to its sensing chamber 25 so that the lowermost tip of the probe is seen to be spaced above the level of conductive fluid by aproximately inch, as shown in FIG. 4. With the platform 10 at the desired level relative to the reference level of the conductive fluid, none of the probe tips will make contact, and the electrical continuity of each sensor 22 will be broken. In this condition, the electrical circuit will be as shown in FIG. 2.

Associated with each sensor 22 is a single-pole doublethrow relay having an output terminal 42 connected to the particular solenoid valve 16 associated with the hydraulic cylinder 15 which controls the movement of the sensor 22 involved. Each relay 41 is also provided with a first set of input terminals 43 and a second set of input terminals 45, which sets are selectively energized by a mode selector switch 46.

In carrying out the invention for lowering the platform 10, the individual probes 26 are adjusted with respect to the reference level of conductive fluid so that none of the probes is in contact with the fluid. In this configuration, the relays 41 are again unenergized, as shown in FIG. 2, and the output terminal 42 of each is switched to its respective second input terminal 45. Because the mode switch 46 is switched to the lowering position, again as shown in FIG. 2, electrical energy is supplied only to the first input terminal 43 of each relay so that none of the normally-opened solenoid valves 16 is energized. The operator may then initiate lowering movement by simply moving the handles of the control valve 17 (which are preferably ganged for ease of operation) in a direction which directs pressure fluid into each of the hydraulic cylinders 15 in a manner which allows lowering of the platform 10.

During lowering, should one portion or corner of the platform 10 begin to lead any other portion, the relative level of conductive fluid will rise in the sensor 22 associated with the leading corner, This will cause a completion of the electrical circuit between the probe 26 and the fluid, thus completing the circuit between the probe lead 38 and the ground lead 40. This energizes the relay 41 associated with that sensor 22, resulting in the switching of electrical energy into the solenoid valve 16 located in the hydraulic circuit of the hydraulic cylinder responsible for the excessive movement. Energization of the solenoid valve 16 interrupts the flow of hydraulic fluid to and from the hydraulic cylinder 15 momentarily until the rest of the platform 10 has caught up with the leading portion, at which point the level of conductive fluid returns to its former plane, breaking the continuity of the responsible sensor 22. The relay 41 thus returns to its normal position, the solenoid valve 16 reopens, and lowering movement then progresses normally.

For operation in the raising direction, the sensors 26 are first set approximately /8 inch below the level of conductive fluid, as shown in FIG. 5. In this position all of the relays 41 remain energized when the platform 10 is in the desired level condition. The mode switch 46, however, is switched to its alternate position in which all of the second input terminals 45 are energized instead of the first input terminals 43 as during lowering operation. This means that the solenoid valves 16 remained in their normally open position when the relays 41 are energized.

Should one portion of the platform 10 rise ahead of the rest of the structure, the excessive raising of its associated sensor 22 will result in the level of conductive fluid dropping below the lowermost portion of the probe 26, interrupting the electrical continuity between the probe lead 38 and the ground lead 40. The associated relay 41 will then open, switching its solenoid valve 16 to the now-energized second input terminal 45, thus closing the solenoid valve and interrupting the flow of hydraulic fluid to the responsible hydraulic cylinder. As before, when the rest of the platform 10 has caught up to the leading portion which initiated the corrective response the conductive fluid again rises to complete the probe circuit, returning the relay to the energized condition and de-ener'gizing the solenoid valve 16.

It will be noted that with the present system individual adjustment of the probes 26 by visual reference to the fluid level in the chambers 25 allows the platform 10 to be intentionally set at a slight angle to the reference level as determined by the conductive fluid. This is desirable in case the vertical supports 11 may themselves not be truly vertical, but at a slight angle. It is possible in this way to adjust the platform 10 to a position which is most compatible for free movement with respect to the supports 11, even if that position is not perfectly horizontal.

We claim:

1. In combination with a movable platfrom guided by a plurality of supports each having an individual electrically controlled power means for raising and lowering an associated portion of said platform, a platform leveling system comprising, in combination, an electrical probe carried by said platform adjacent each support, the lowermost point of each probe being disposed in a common plane, a fluid sensing chamber associated with each probe, fluid conduit means continuously interconnecting each of the sensing chambers in a closed fluid circuit, electrically conductive fluid filling the conduit means to a predetermined level relative to the common plane of the probes, and control means associated with each probe and the power means of its adjacent support for controlling the rate of platform movement eflected by the power means, said control means being responsive to variations in the electrical continuity between its probe and the conductive fluid, whereby variation of the level of conductive fluid relative to the lowermost point of any of the probes in a predetermined direction will eflect a compensatory variation in its associated power means to cause the conductive fluid to flow back through the closed fluid circuit in a direction which will eliminate the variations in electrcal continuity between the probes and the conductive fluid.

2. The combination defined in claim 1 in which said control means associated with each of said probes includes an electrically controlled power cut-01f means and a relay means effective to switch the power cut-off means between either of a first input terminal when the probe is in contact with the conductive fluid or a second input terminal when the probe is not in contact with the conductive fluid, and a source of electrical power alternately switchable between either the said first input terminals of the several relay means for operation during raising of the platform, or the said second input terminals for operation during the lowering of the platform.

3. The combination defined in claim 2 in which each of said power means includes a hydraulic cylinder connected to a source of pressure fluid through a control valve, and each of said power cut-off means includes an on-oif solenoid valve.

4. The combination defined in claim 1 in which each of said probes is individually adjustable in elevation relative to its associated sensing chamber for selectively positioning the lowermost tip of the probe above or below the level of the conductive fluid.

5. The combination defined in claim 4 in which each of said sensing chambers has a transparent window opening for visually observing the level of conductive fluid relative to the probe.

6. A method for leveling a platform during movement relative to a plurality of vertical supports each having individual power raising and lowering means, said platform having an electrical probe adjacent each support, a sensing chamber associated with each probe, and fluid conduit means continuously interconnecting each sensing chamber and filled with electrically conductive fluid, the method comprising the steps of positioning the lowermost tip of each probe in a common horizontal reference plane at a predetermined position relative to the level of conductive fluid, sensing variations in the level of conductive fluid from each probe tip due to a relative lead in vertical movement of one probe relative to the other probes, decreasing the rate of movement of the one power means associated with said one probe relative to the other power means, sensing the return of said one probe to said predetermined position relative to the horizontal reference plane, and restoring said one power means to its prior rate of movement.

7. The method of claim 6 in which the probe tips are positioned at a predetermined distance below the level of conductive fluid for raising operation whereby the electrical circiut between the probes and fluid is interrupted upon the unequal increase in upward movement of one probe relative to the other probe.

8. The method of claim 6 in which the probe tips are positioned at a predetermined distance above the level of conducted fluid for lowering operation whereby the electrical circuit between the probe and fluid is completed upon the unequal increase in downward movement of one probe relative to the other probes.

References Cited UNITED STATES PATENTS 3/ 1941 Anthony 187-859 5/ 1962 Nesbitt 61-46.5

REINALDO P. MACHADO, Primary Examiner 

